Question

我有以下4个班级： CarApplication [主类]，本田延伸车辆，车辆，和 VehicleType

这是车辆类：

import org.springframework.beans.factory.annotation.Autowired;
public class Vehicle {

    @Autowired
    public VehicleType type;
    public String getType() {
        return type.getType();
    }
}

这是本田班：

public class Honda extends Vehicle{

    private String motor = "honda motor";

    public void displayMotor(){
        System.out.println(motor);


        System.out.println(getType()); 
    }

}

这是VehicleType类：

public class VehicleType {

    private String type;

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }


}

这是主要课程：

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class CarApplication {

    public static void main(String[] args) {


        ApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml");

        Honda honda = (Honda)ctx.getBean("honda");
        honda.displayMotor();



    }

}

以下是我的Spring上下文文件：

<?xml version="1.0" encoding="UTF-8"?>
 <beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context-3.0.xsd">


    <bean id="honda" class = "mq.spring.practice1.Honda" parent ="vehicle"/>
    <bean id="vehicle" class = "mq.spring.practice1.Vehicle"/>
    <bean id ="type" class="mq.spring.practice1.VehicleType">
        <property name="type" value="car"/>
    </bean>






 </beans>

运行时出现以下错误：

Exception in thread "main" honda motor java.lang.NullPointerException
  at mq.spring.practice1.Vehicle.getType(Vehicle.java:11)
  at mq.spring.practice1.Honda.displayMotor(Honda.java:11)
  at mq.spring.practice1.CarApplication.main(CarApplication.java:15)

我调试它并发现公共VehicleType类型为null。我做错了吗？

由于

Answer 1

在下面添加上下文文件：

<context:annotation-config />

需要激活已在应用程序上下文中注册的bean中的注释

Spring继承不起作用

1 个答案: